S Palea, N Gilles, V Guilloteau, M Guérard, P Lluel. Comparison of the effects of AdTx1 and tamsulosin on the increase in intra-urethral and arterial pressures induced by phenylephrine in anesthetized male rats. World Congress of Basic and Clinical Pharmacology, Copenhagen (Denmark) July 2010.

Abstract

Background and Purpose

ρ-Da1a, a 65 amino-acid peptide, has subnanomolar affinity and high selectivity for the human α1A-adrenoceptor subtype. The purpose of this study was to characterize the pharmacological effects of ρ-Da1a on prostatic function, both in vivo and in vitro.

Experimental Approach

ρ-Da1a was tested as an antagonist of adrenaline-induced effects on COS cells transfected with the human α1A-adrenoceptor as well as on human isolated prostatic adenoma obtained from patients suffering from benign prostatic hyperplasia. Moreover, we compared the effects of ρ-Da1a and tamsulosin on phenylephrine (PHE)-induced increases in intra-urethral (IUP) and arterial pressures (AP) in anaesthetized rats, following i.v. or p.o. administration.

Key Results

On COS cells expressing human α1A-adrenoceptors and on human prostatic strips, ρ-Da1a inhibited adrenaline- and noradrenaline-induced effects. In anaesthetized rats, ρ-Da1a and tamsulosin administered i.v. 30 min before PHE significantly antagonized the effects of PHE on IUP. The pKB values for tamsulosin and ρ-Da1a for this effect were similar. With regards to AP, ρ-Da1a only reduced the effect of PHE on AP at the lowest dose tested (10 μg·kg−1), whereas tamsulosin significantly reduced PHE effects at doses between 10 and 150 μg·kg−1.

Conclusions and Implications

ρ-Da1a exhibited a relevant effect on IUP and a small effect on AP. In contrast, tamsulosin antagonized the effects of PHE on both IUP and AP. We conclude that ρ-Da1a is more uroselective than tamsulosin. ρ-Da1a is the most selective peptidic antagonist for α1A-adenoceptors identified to date and could be a new treatment for various urological diseases.